DESCRIPTION: The pathogenesis of myasthenia gravis (MG) involves an antibody-mediated autoimmune response directed against acetylcholine receptors (AChR). Although current treatment of MG with immunosuppressive agents is reasonably effective, it has important drawbacks, including overall suppression of the immune system, and other adverse side effects. The goal of specific immunotherapy has remained elusive. Since the pathogenic AChR antibody response is T cell dependent, inactivation or elimination of AChR-specific T cells interrupts the immune response, with resulting clinical benefit. However, the fact that T cell responses to AChR are highly heterogeneous presents a strategic problem in designing specific immunotherapy. This proposal will explore and capitalize on a novel strategy of safe stimulation to target the entire spectrum of AChR-specific T cells, using denatured AChR (denAChR), in conjunction with genetically engineered agents that inactivate and/or eliminate the specifically stimulated T cells. The studies will be carried out in Lewis rats with experimental autoimmune MG (EAMG). DenAChR stimulates AChR-specific T cells as strongly as native AChR, but its reduced and non-pathogenic AChR antibody response avoids the risk of exacerbating MG. Stimulation is a necessary condition for the action of the therapeutic agents. CTLA4Ig is a soluble recombinant protein that blocks the B7 family of costimulatory molecules, and may induce anergy in antigen-stimulated T cells. Preliminary studies suggest that CTLA4Ig prevents primary EAMG and inhibits secondary EAMG, with interesting changes in the AChR antibody isotypes, suggestive of a switch in T helper cells from Th1 to Th2 type. DAB389IL2 is a fusion protein that binds to IL2 receptors on antigen-activated T cells, and kills them via a lethal diphtheria toxin moiety. Preliminary studies using DAB389IL2 in vitro and in vivo show marked inhibition of immune responses to AChR. Combined use of CTLA4Ig + DAB389IL2 appears to be even more potent, with a powerful effect on the difficult-to-treat secondary immune response to AChR. We will study the effects of this strategy on antibodies to Torpedo and autoantibodies to rat